A semiconductor memory device, such as a DRAM (Dynamic Random Access Memory), includes memory cell arrays each having memory cells disposed at intersections between word lines and bit lines. Various conditions in the memory device, such as operating temperatures and voltages in the power supply etc., may affect the performance of the memory device. For example, the impedance of the input/output (IO) circuit may be affected by the varying power supply voltage or temperature. As such, an impedance calibration (e.g., ZQ calibration) is periodically performed in the memory device to compensate for the variations of impedance of the IO circuit. However, when a ZQ calibration is performed, a higher power voltage may be required, and the performance of the semiconductor device may be adversely affected.